%IBVS article on WW Cyg, EQ Tau, and T Lmi by Buckner and Nellermoe.
%Draft of 16 Feb 98 : modify re refereee comments

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\begin{document}
\IBVShead{4559}{24 February 1998}

\IBVStitle{ECLIPSE TIMING OBSERVATIONS OF THREE CLOSE BINARIES}

\IBVSauth{M.~BUCKNER, B.~NELLERMOE, R.~MUTEL}

\IBVSinsto{Van Allen Observatory, University of Iowa, Iowa City, IA, 
52242, email: ccdoper@astro.physics.uiowa.edu}

\SIMBADobj{WW Cyg, EQ Tau, T LMi}
\IBVSkey{photometry}
\IBVSabs{High precision timing observations of eclipse minima}
\IBVSabs{are given for the close eclipsing binaries T LMi, EQ Tau, and WW Cyg.}

% Some defs for ra, dec
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\def\ra[#1 #2 #3]{#1\sup{h}#2\sup{m}#3\sup{s}}

\begintext

T Leonis Minoris, EQ Tauri, and WW Cygni are frequently observed close
eclipsing binaries.  These systems are on the AAVSO list of eclipsing
binaries (Baldwin and Samolyk 1993). The AAVSO database of O$-$C
observations (largely from visual timings) showed some evidence for
either period changes or incorrect periods in all three systems. 

The present note describes CCD photometry of T LMi, EQ Tau, and WW Cyg
using the University of Iowa's Automated Telescope Facility located in
Iowa City, Iowa.  The system consists of an 18cm refractor, a
Spectrasource HPC-1CCD camera (format $512 \times 512$ binned pixels,
3\farcs 00 per pixel), and a Johnson $R$-band filter. A series of 60
second exposures of a field containing the target star as well as 
check and comparison stars was repeated every two minutes for three
hours.  Differential aperture photometry was performed by an automated
procedure after aligning all images to a common stellar reference.  No
air mass or color corrections were applied. At $R$ band, we estimate this
will introduce errors less than 0.05 mag.

The central time and uncertainty of each eclipse minimum was determined
by a least-squares algorithm which `folds' the light curve about the
center of the eclipse, i.e.  setting the heliocentric Julian date (HJD)
at the time of minimum to zero and plotting the differential magnitude
versus the absolute value of the HJD to produce a folded light curve for
each night.  As our original curves were almost perfectly symmetric, any
shift in the minimum HJD greater than $\pm$0.0005 HJD caused noticeable
discrepancies between the two halves.

For all three stars, we used the published ephemerides given by
Danielkiewicz-Krosniak and Kurpinska-Winiarska (1996; hereafter DK96) to
determine O$-$C values.  We determined new periods by fitting the AAVSO
observations along with the minima reported in this note. We used a
least-squares linear regression weighted by the uncertainty of each
observation. For the AAVSO data, we assumed the mean uncertainty
$\pm0.003$ days.

\vskip 2mm
{\bf T LMi}
\vskip 2mm

For T LMi (A0, R=12.95, 9\hr 48\mm 28\fsec 54, +33\deg 17\arcm 20\arcs, J2000) we used
the nearby Guide Star Catalog (GSC) star 2505.1038 9\hr 48\mm 35\fsec 4,
+33\deg 13\arcm 06\arcs) and GSC\,2504.252 (9\hr 47\mm 53\fsec 0, +33\deg 16\arcm 57\arcs) as
the check and comparison star respectively.  T LMi system was observed
during the night of 15 February 1997 UT.  We observed a primary minimum
at HJD = 2,450,494.8857$\pm$0.0005 (Figure 1a). The O$-$C plot, using the
AAVSO database, and a period $P=3.019846$ days and JD0=2,446,910.332 (DK96)
is shown in Figure 2a, along with the best-fit linear regression. The
revised period is slightly shorter, $P=3.019841\pm0.0000015$ days.

\epsfxsize=3.95in
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\IBVSfig{3.95in}{4559-f1c.eps}{Light curves for T LMi (primary eclipse), 
EQ Tau (secondary eclipse), and WW Cyg (primary eclipse)}  
\vfill\eject


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\centerline{\epsffile{4559-f2a.eps}}
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\vskip -0.2in
\IBVSfig{3.95in}{4559-f2c.eps}{O$-$C plots for T LMi, EQ Tau, and WW Cyg. 
Historical data are from the AAVSO Archives (Observed Minima Timings of 
Eclipsing Binaries). The straight lines are weighted least-squares linear 
regressions}  
\vfill\eject

{\bf EQ Tau}
\vskip 2mm
For EQ Tau (G1, R=11.07, 3\hr 48\mm 13\fsec 38, +22\deg 18\arcm 51\farcs 4, J2000) we
used the nearby star GSC\,1260.642 (3\hr 48\mm 42\fsec 9, +22\deg 21\arcm 32\arcs) and
GSC\,1260.575 3\hr 48\mm 16\fsec 4, +22\deg 17\arcm 30\farcs 2) as check and comparison
star respectively. EQ Tau was observed during the night of 09 November
1996 UT. We observed a secondary minimum at HJD =
2,450,396.9250$\pm$0.0005 (Figure 1b).  The O$-$C plot, using the AAVSO
database, a period $P=0.3413485$ days and $JD0=2,440,213.325$ (DK96), is
shown in Figure 2b. The linear regression fit resulted in a slightly
shorter period $P=0.3413471\pm0.0000001$ days.

\vskip 2mm
{\bf WW Cyg}
\vskip 2mm

For WW Cyg (B8V+, R=10.94, 20\hr 04\mm 02\fsec 69, +41\deg 35\arcm 17\arcs, J2000) we used the nearby stars GSC\,3158.220 (20\hr 04\mm 25\fsec 2, +41\deg 30\arcm 16\arcs)
and GSC\,3158.1498 20\hr 04\mm 12\fsec 5, +41\deg 33\arcm 06\arcs)
as the check and comparison star respectively. We observed a primary
minimum at HJD = 2,450,387.6074$\pm$0.0005 (Figure 1c).  The O$-$C plot,
using the AAVSO database, a period $P=3.317769$ days and
JD0=2,440,377.886 (DK96), is shown in Figure 2c. The linear regression
fit resulted in a slightly longer period $P=3.3177779\pm0.0000007$ days.

Table 1 summarizes the new ephemerides determined for all three systems.

\vskip 1cm
\centerline{Table 1. Revised Linear Ephemerides}
\vskip 3mm
\begin{center}
\begin{tabular}{lcc}
\hline
Star &  JD0  &  P(days) \\ \hline
T LMi &  $2,450,494.8857\pm0.0005$ & $3.019841\pm0.0000015$ \\
EQ Tau & $2,450,397.0957\pm0.0005$ & $0.3413471\pm0.0000001$ \\
WW Cyg & $2,450,387.6074\pm0.0005$ & $3.3177779\pm0.0000007$ \\ 
\hline
\end{tabular}
\end{center}

\vskip 1cm

This research has been supported by the Iowa Space Grant Consortium and
the National Science Foundation.

\vskip 5mm

\references

Baldwin, M. and Samolyk, G. 1993, AAVSO Observed Minima Timings of
Eclipsing Binaries No.\,1

Danielkiewicz-Krosniak, E. and Kurpinska-Winiarska M., T. 1996, SAC -
Supplemento ad Annuario Cracoviense, 67. (DK96)



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